Waiver typically adds additional year or more to processing times.
You'd get a better chance of waiver approval if you have a proven track record of:
1) Refusing vaccines throughout your life (e.g. you never got any vaccines)
2) You're a member of religious organization or believer who takes active participation in it
3) Some examples of what religion says about vaccinations. Quotes from holy books, religious leaders etc.
I'm not an expert in this area, but I'd imagine there's a high burden of proof. Protecting US public health is one the top priorities for US government, your reasons must be compelling to get an exception.
You're gotta be pretty sure your religion doesn't allow vaccinations. If unsure, the chances of approval are lower.